1. Field of the Invention
Embodiments of the invention relate to the field of semiconductor, and more specifically, to semiconductor fabrication.
2. Description of the Related Art
Low dielectric constant (low-k) materials are used in interlayer dielectrics (ILD) in semiconductor devices to reduce propagation delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between the metal lines should decrease to maintain the improvement. The eventual limit for the dielectric constant is k=1, which is the value for vacuum. This can be achieved by producing a void space between the metal lines, effectively creating an air gap. Air itself has a dielectric constant very close to 1. One major problem with air gap technology is the removal of sacrificial material to fabricate multi-layer structures.
Existing techniques to remove sacrificial material have a number of drawbacks. Use of plasmas may be destructive to the metal lines. Wet etches have many problems, including capillary forces that can break the lines apart, the difficulty in removing material from small features, and the difficulty in removing the wet etch chemical once it has been introduced. Thermal decomposition presents problems in that the sacrificial material must remain stable during high temperature fabrications stages, but it may decompose rapidly at normal temperatures that will not destroy the device.